Mail insertion machines implementing continuous motion, or at least substantially continuous motion, have been developed in the past. A basic function of such machines is to establish a flow of inserts, such as documents or other sheet-type products, establish a flow of envelopes, and combine both flows into a single, common feed path. Once a given insert and a given envelope enter the common feed path, the insert must be inserted into the opened envelope at a common insertion point, after which point the stuffed envelope is transported downstream along a single output path for subsequent processing. In the continuous motion-type insertion machine, an effort is made to increase throughput by reducing the number of times the feed path must be stopped and/or reducing the duration of the stoppage. This has been accomplished by transporting the inserts along the feed path at a higher speed than the envelopes, or by at least accelerating the inserts in relation to the envelopes, so that a given insert “overtakes” or catches up to its corresponding, aligned envelope and is completely inserted into the envelope with minimal stoppage of the flow of either the insert or the envelope along the feed path.
As will be appreciated by persons skilled in the art, the successful operation of the above-described mail insertion machine depends upon adequate synchronization of the various moving components involved in carrying out the insertion process. It is often desirable to change the overall speed of the machine, such as when differently-sized inserts and/or envelopes are to be processed, in which case steps must be taken to ensure all moving components are still synchronized at the different machine speed. For example, in U.S. Pat. No. 3,423,900 to Orsinger, a continuous motion inserting machine is disclosed in which all moving components, such as the envelope feeding and insert feeding mechanisms, are entirely mechanically linked together. It can be appreciated that any change in the operating speed of such a machine would necessitate laborious mechanical adjustments of several components in order to preserve synchronization.
Even with the modern development of servo motors and motion controllers, satisfactory methods have not heretofore been developed for interfacing such modern control components with mail inserting machines for the purpose of maintaining synchronization in response to varied machine speeds, particularly in the context of continuous motion-type inserting machines. Indeed, the use of modern machine components often exacerbates the problem of synchronization. This has been particularly observed in the case of modern, variable-speed, cyclical mail inserting machines. During the operation of such machines, the duration of time between certain events vary according to overall machine speed. These machines, however, contain both servo motor-driven components or assemblies and actuator-driven components. The respective operating speeds of the motor-driven components or assemblies can be easily controlled and varied by a motion controller. At the same time, however, the respective activation speeds of the actuator-driven components (i.e., the duration of time required for the component to move from its inactive or OFF state to its active or ON state) are inherently fixed and thus cannot be forced to vary. It can therefore be appreciated that the use of variable-speed components together with fixed-speed components renders synchronization difficult.
As an example, a variable-speed cyclical machine contains one or more rotating assemblies or components whose respective operating speeds somehow depend on the master speed of the machine (such as through actual linkage to the main drive shaft of the machine, or simply due to the requisite timing relation among the various moving components of the machine). If, for example, the machine is running at a machine speed of 1 cycle per second, the machine takes 250 milliseconds to move through 90 degrees of its machine cycle. If the speed of the machine is increased to 5 cycles per second, the machine now takes only 50 milliseconds to move through the same 90 degrees of the machine cycle at this new machine speed. As part of its operation, the machine can further contain at least one component driven by a solenoid. As a general matter, solenoids take a constant duration of time to become active (e.g., the time required for the plunger of the solenoid to fully extend outwardly and actually cause the required actuation event), and this activation time is completely independent of the machine speed. In the present example, the solenoid takes 50 milliseconds to become active. The successful operation of this machine dictates that the solenoid be fully active at a given point in time during the machine cycle (e.g., 90 degrees). In addition, the operation requires that the solenoid be inactive until another given point during the cycle (e.g., 85 degrees). Accordingly, there exists no common point during any machine cycle at which the solenoid can be turned ON for all speeds over which the machine is intended to operate.
Continuing with the present example, at the machine rate of one cycle per second, the machine travels 18 degrees (90 degrees divided by 5) in 50 milliseconds (250 milliseconds divided by 5). At this rate, the solenoid must be activated, or fired, at 72 degrees (90 degrees minus 18 degrees) in order for the solenoid to be fully activated at 90 degrees. This is because, upon the initial energizing of this particular solenoid, it always takes 50 milliseconds for the solenoid to become completely active. In the present example, at 1 cycle per second, 50 milliseconds corresponds to 18 degrees of rotation through the machine cycle. As discussed above, at the machine rate of 5 cycles per second, the machine travels 90 degrees in 50 milliseconds. Hence, at this increased machine cycle speed, the solenoid must fire at 0 degrees in order to be fully activated at 90 degrees (because at 5 cycles per second, 50 milliseconds corresponds to 90 degrees, instead of 18 degrees in the case of a cycle speed of 1 cycle per second).
It can thus be seen that if the machine has been operating at 5 cycles per second and the solenoid is correctly set to fire at 0 degrees at that machine speed, the solenoid will fire at the wrong time if the machine speed is changed. In the specific example, if the machine speed is decreased to 1 cycle per second and the solenoid fires at 0 degrees, the solenoid will become fully active at 18 degrees, which is much too early during the machine cycle if the machine is running at 1 cycle per second. One the other hand, if the solenoid is set to fire correctly (at 72 degrees) while the machine speed is 1 cycle per second, and the machine is actually running at 5 cycles per second, then the solenoid will not be fired until the machine cycle reaches 72 degrees and thus will not be active until 162 degrees (72 degrees plus 90 degrees, where 90 degrees corresponds to the fixed activation time of the solenoid, 50 milliseconds, at the machine speed of 5 cycles per second), which is much too late.
In either scenario, the solenoid will fire, and thus eventually become fully active, at the wrong point in time during the operating cycle of the machine. In the context of a continuous motion inserting machine, as well as in other types of machines requiring coordination and synchronization of different moving components, the improper activation time of the solenoid could result in an insert or an envelope failing to be presented at the proper time into the feed path, an envelope failing to open, an insert failing to be completely inserted into an envelope prior to ejection to downstream processes, and so on.
One approach to maintaining proper control and synchronization in a variable-speed inserter machine is disclosed in the following series of related disclosures: U.S. Pat. Nos. 5,823,521; 5,941,516; 5,949,687; 5,954,323; and 5,975,514; all of which issued to Emigh et al, and are owned by Bell & Howell Mail and Messaging Technologies Co. In the main embodiment disclosed in these patens, a Phillipsburg-type mail inserter machine has twelve stations or subassemblies, all of which operate (i.e., are activated and deactivated) in timed relation over the 360-degree timing cycle of the inserter machine. The respective operations of these stations is put under computer-driven, adaptive control, in order to compensate for the electromechanical time lags exhibited by certain components such as pneumatic cylinders that require extension and retraction. As a result, the ON-OFF control signal used to initiate and terminate the respective electromechanical functions of the actuator-type components can be adjusted in response to a change in machine speed, thereby maintaining correct timing of the various components.
In the Emigh et al. patents, the adaptive control is implemented by programming “look-up” speed tables into the control software executed by the computer. These speed tables include the correct start angles (i.e., the timing for an ON control signal) and stop angles (i.e., the timing for an OFF control signal) for each station requiring such control. A “low” speed table, derived empirically, is provided for the machine operating within the range of 0-2000 cycles per hour. Additionally, the respective time lags (or activation times) for the various actuator-type components are empirically measured, and the resulting value stored in an “operational delay” look-up table. The values from the operational delay tables are used together with the cycle speed of the machine to calculate adaptive adjustment factors, which in turn are used in further calculations to determine new start and stop angles for a different cycle speed. These new values are entered into a new speed table. This process is carried out until five successive speed tables are generated, each corresponding to a cycle speed range of 2,000 cycles per hour in width, such that the five speed tables cover the operation of the machine over a total range of 0-10,000 cycles per hour. The mail inserter machine is ready for operation only after all five predetermined speed tables have been stored in memory.
During operation of the mail inserter machine disclosed in the Emigh et al. patents, the computer samples the output of a tachometer such as an absolute optical encoder interfaced with the main drive shaft of the machine. This sampling is rigidly performed at constant intervals as dictated by a clock speed, regardless of what the machine is actually doing. In the specific embodiment disclosed, the sampling is taken without exception every 100 milliseconds. Based on the cycle speed measured by the encoder, the computer selects the appropriate speed table and uses the values from the selected speed table to determine the proper control signals to be issued to the actuator-type components. As an alternative, the computer can use the low speed table and the operational delay table to update a new speed table every 100 milliseconds. It is disclosed, however, that this latter method has the disadvantage of possibly slowing down the computer due to the CPU having to make repetitive calculations every 100 milliseconds.
It would be therefore be advantageous to provide a method and apparatus for more precisely controlling and adjusting actuators in response to variable machine speeds on a substantially continuous basis, particularly in the operating environment of continuous motion inserting machines, in order to more easily and precisely maintain synchronization after a speed adjustment occurs, and further to ensure more consistent performance during ramp-up and shut-down portions of the machine cycle.